The Sansa Clip is a great mp3 player. All it does is play music (which is a big plus in my book), it's really small so it's great for running or other similar things, and the physical buttons make it really easy to use one-handed without looking at the screen.

When I got my first good-quality smartphone, I had planned on moving all my music over to it, but stopped when I found that the Clip was really a better device for music.